“Crying happy tears” or “mass murder?” A comparative thematic and rhetorical analysis of social media perspectives on a future HIV vaccine (Preprint)

BACKGROUND As the prospect of an HIV vaccine nears reality, understanding public discourse around the vaccine is essential for informing communication strategies and addressing misinformation. Social media platforms are influential spaces where public narratives form, yet little research has examined discourse around an HIV vaccine, especially on TikTok. OBJECTIVE To compare and characterize public discourse about a future HIV vaccine across Twitter and TikTok, identifying prevailing themes, sentiments, and rhetorical strategies to inform public health communication. METHODS From over 400,000 tweets and 65,000 TikTok comments, we analyzed the 1,000 most-liked posts on each platform using natural language processing and coded the top 500 posts for rhetorical strategies, sentiment, and themes. RESULTS Our findings reveal expressions of hope and trust in science on both platforms, as well as concerns about institutional corruption and conspiracy theories, such as the belief that the HIV vaccine responds to harm caused by the COVID-19 vaccine. Tweets tended to be more linguistically complex and yielded richer insights, while TikTok comments were shorter and more difficult to interpret without video context. Key rhetorical strategies included conspiracy theories, post hoc reasoning, and emotional appeals. CONCLUSIONS This study underscores the need for platform-specific communication strategies to address misinformation and build public trust. Findings offer timely insight into emerging HIV vaccine discourse and highlights actionable opportunities for public health stakeholders to build trust and combat misinformation in advance of vaccine rollout.